Date: Tue, 16 Jul 2013 12:42:14 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: aurfalien <aurfalien@gmail.com> Cc: freebsd-questions@freebsd.org, Shane Ambler <FreeBSD@ShaneWare.Biz> Subject: Re: to gmirror or to ZFS Message-ID: <alpine.BSF.2.00.1307161239580.82091@wonkity.com> In-Reply-To: <C13CC733-E366-4B54-8991-0ED229932787@gmail.com> References: <4DFBC539-3CCC-4B9B-AB62-7BB846F18530@gmail.com> <alpine.BSF.2.00.1307152211180.74094@wonkity.com> <976836C5-F790-4D55-A80C-5944E8BC2575@gmail.com> <51E51558.50302@ShaneWare.Biz> <C13CC733-E366-4B54-8991-0ED229932787@gmail.com>
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On Tue, 16 Jul 2013, aurfalien wrote: > On Jul 16, 2013, at 2:41 AM, Shane Ambler wrote: >> >> I doubt that you would save any ram having the os on a non-zfs drive as >> you will already be using zfs chances are that non-zfs drives would only >> increase ram usage by adding a second cache. zfs uses it's own cache >> system and isn't going to share it's cache with other system managed >> drives. I'm not actually certain if the system cache still sits above >> zfs cache or not, I think I read it bypasses the traditional drive cache. >> >> For zfs cache you can set the max usage by adjusting vfs.zfs.arc_max >> that is a system wide setting and isn't going to increase if you have >> two zpools. >> >> Tip: set the arc_max value - by default zfs will use all physical ram >> for cache, set it to be sure you have enough ram left for any services >> you want running. >> >> Have you considered using one or both SSD drives with zfs? They can be >> added as cache or log devices to help performance. >> See man zpool under Intent Log and Cache Devices. > > This is a very interesting point. > > In terms if SSDs for cache, I was planning on using a pair of Samsung Pro 512GB SSDs for this purpose (which I haven't bought yet). > > But I tire of buying stuff, so I have a pair of 40GB Intel SSDs for use as sys disks and several Intel 160GB SSDs lying around that I can combine with the existing 256GB SSDs for a cache. > > Then use my 36x3TB for the beasty NAS. Agreed that 256G mirrored SSDs are kind of wasted as system drives. The 40G mirror sounds ideal.
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